Resin particles have become important and been used for many applications.
The resin particles are produced by many methods. One of the most common methods is a grinding method wherein resin particles are prepared by blending a thermoplastic resin at a melting condition and then grinding. There are some applications which require employment spherical resin particles. The resin particles obtained by the grinding method, however, are too flat to apply such applications.
A method recently proposed includes a soap-free polymerization method or a seed-emulsion polymerization method. These methods produce spherical resin particles, but, in order to obtain particles having a particle size of 1 to about 50 microns, it is required to repeat the polymerization reaction several times. The resin particles thus obtained may raise blocking. Also, the system of preparing the particles is electrically stabilized, so that the obtained particles may have strong electric charge. The particles are limited in their applications because of the strong charges.
A suspension polymerization method may also be employed, but the particle size distribution of the obtained particles is very broad and blocking often occurs.
When the resin particles are used for toner which is one of their main usages, blocking has to be effectively prevented. In order to prevent the blocking of toner, it has been proposed to have a high molecular weight or glass-transition temperature of the resin. This, however, raises the fixing temperature and causes cold offset.